This application claims priority to German Patent Application No. 10145430.9 filed Sep. 14, 2001, which application is herein expressly incorporated by reference.
The invention relates to a torque limiting coupling, especially, in a drive transmission unit of agricultural implements. Torque limiting couplings prevent damage or destruction of agricultural implement due to overloading. The torque limiting coupling separates the driving side from the agricultural implements when the torque necessary to drive the agricultural implement exceeds a threshold value and may lead to damage of the implement. This may occur when the agricultural implement is blocked.
DE 30 34 606 A1 illustrates a torque limiting coupling with a coupling hub and a coupling sleeve. The coupling hub and sleeve are rotatably arranged around a longitudinal axis. The coupling hub has through holes which adjustably hold transfer elements parallel to the longitudinal axis. The transfer elements engage, in a torque transmitting position, recesses corresponding to the through holes. A switching disk is acted upon axially by a spring and is supported on the transfer elements. Thus, the transfer elements are held in the recesses. When a predetermined torque is exceeded, the transfer elements are pushed axially against the spring force of the spring out of the recesses. The transfer elements roll off on a side face of the coupling sleeve and turn the switching disk into a position where the transfer elements engage in recesses of the switching disk. In this position the coupling hub is drivingly separated from the coupling sleeve. Thus, torque can not be transmitted between the coupling hub and the coupling sleeve. Furthermore, a switching cam projects radially outwardly from the external circumference of the switching disk. A switching ram is adjustably arranged between a release position and a retaining position. In the retaining position the switching ram interacts with the switching cam. Accordingly, when the torque limiting coupling rotates, the switching disk transfers to its freewheeling position. Thus, torque transmission is interrupted. A return cam on the coupling nose of the switching ram is moved back into a release position after rotation of the switching disk. A disadvantage of this embodiment is, that, when switching off the torque limiting coupling the driven masses of the agricultural implement are lagging. Retention of the driven masses of the agricultural implement need to be achieved by a separate unit.
It is an object of the present invention to provide a torque limiting coupling that interrupts the torque transmission when an overload occurs, and stops the driven masses.
The object is achieved by a torque limiting coupling including a longitudinal axis around which the torque limiting coupling is rotatably arranged. A coupling hub has through holes distributed around its circumference. Transfer elements are adjustably held parallel to the longitudinal axis in the through holes. A coupling sleeve drives the coupling hub in one rotational driving direction. The coupling sleeve has first recesses corresponding to the through holes.
A switching disk is rotatably arranged between a torque transmitting position and a freewheeling position relative to the coupling hub. The switching disk is acted upon by a spring acting in the circumferential direction to the torque transmitting position. The switching disk urges, via an axially acting spring force, the transfer elements in the direction towards the coupling hub. The transfer elements engage the recesses of the coupling sleeve for torque transmission. The transfer elements disk roll off the switch disk when a predetermined nominal torque is exceeded. Thus, the transfer elements move from the torque transmitting position to the freewheeling position. The switch disk has second recesses corresponding to the through holes. The transfer elements engage the second recesses in the freewheeling position.
A locking pawl is movable between a release position and a retaining position. The locking pawl interacts with a radial selector face on the circumference of the switching disk in the retaining position. Accordingly, the switching disk can be transferred from the torque transmitting position to the freewheeling position. The locking pawl interacts with a radially extending first retaining face of the coupling hub in the retaining position. Accordingly, the coupling hub is retained (held) against rotation around the longitudinal axis in the rotational driving direction. The locking pawl has a mechanism that interacts with the coupling hub in the retaining position of the locking pawl. Here, the coupling hub is retained against rotation opposite to the rotational driving direction.
Therefore, the torque limiting coupling according to the invention serves two functions. The first function is separation of the coupling hub from the coupling sleeve when an overload occurs. Thus, torque is not transmitted between the coupling hub and the coupling sleeve. Here, the torque limiting coupling is designed so that when the relative rotational speed between the coupling hub and the coupling sleeve is reduced, the switching disk is moved back to the torque transmitting position due to the spring acting in a circumferential direction. Accordingly, the torque limiting coupling can only be switched on by reducing the torque. Without torque reduction the torque limiting coupling has to be manually adjusted.
The second function is switching off the torque limiting coupling. This occurs after transferring the locking pawl into the retaining position. Accordingly, the switching disk is moved into its freewheeling position and the driven coupling hub is retained against rotation by the locking pawl. The locking pawl is pivotably mounted on a frame of an agricultural implement. Thus, the forces are supported on the frame of the agricultural implement when stopping the coupling hub and the connected driven masses of the agricultural implement.
The torque limiting coupling according to the invention enables an emergency switching-off of the drive. The locking pawl can be released by a manually operable switch. Thus, the operating personnel can manually stop the agricultural implement in an emergency situation. Furthermore, it is possible to actuate the locking pawl by a sensor unit. The sensor observes the working area and the area of the agricultural implement. If a foreign body enters this danger area, the locking pawl is released.
Furthermore, the locking pawl ensures, via interaction with the coupling hub, that the driven masses are prevented from turning back. A turn back may occur when the torque of the coupling sleeve is reduced. Here, the spring acting in the circumferential direction causes the coupling hub to turn back while the switching disk is supported on the locking pawl. Due to this, the torque limiting coupling would again be switched on. The coupling hub would again be driven in the rotational driving direction. Further, due to the resulting relative rotation of the coupling hub to the switching disk, the torque limiting coupling would be switched off. In a low torque range this procedure would be continually repeated.
In the freewheeling position of the switching disk, the locking pawl engages with a catch lug directed to the longitudinal axis in a radial retaining groove of the coupling hub. The locking hub forms the first retaining face and a second retaining face which prevent a rotation of the coupling hub in both rotational directions.
Alternatively, in the freewheeling position of the switching disk, the locking pawl may be supported with a catch lug directed radially in the direction of the torque limiting coupling on the first retaining face of the coupling hub. Further, the locking pawl may be supported with a spring on a radial second retaining face.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.